On July 23, Dr. Kent Brantly woke up with a fever. He immediately quarantined himself, and three days later a test confirmed his nightmare. He had the Ebola virus.

Brantly, 33, emailed a friend and said that he was “terrified,” for he knew better than anyone the horror of the virus. He had been treating patients in West Africa with it for many weeks, watching as they vomited, hemorrhaged internally and sometimes bled from multiple orifices – then weakened and died.

Some people have blamed Brantly and another American missionary infected, Nancy Writebol, for bringing the danger to themselves, even objecting to their return to Atlanta to be treated for the disease at Emory University Hospital. For example, Donald Trump argued that Brantly and Writebol should not be brought back to the United States because of the risks involved.

“People that go to far away places to help out are great – but must suffer the consequences!” Trump tweeted.

On the contrary, this Ebola outbreak underscores why we have not only a humanitarian interest in addressing global health, but also a national interest in doing so. Brantly and Writebol are moral leaders in this effort and underscore the practical imperative of tackling global contagions early on. They deserve our gratitude and admiration because in Liberia they were protecting us as well as Liberians.

The human mind is very sensitive to threats from the likes of al-Qaida. We are less attuned to public health threats, even those that claim more lives: Some 15,000 people with AIDS still die in the United States every year, according to the Centers for Disease Control and Prevention. It’s better to address a contagious disease at its source rather than allow it to spread.

“If we don’t fight to contain it there, we’re going to fight to contain it somewhere else,” notes Ken Isaacs of Samaritan’s Purse, the Christian aid group for which Brantly works.

The World Bank has pledged $200 million to try to control the Ebola outbreak, but a tiny fraction of that sum might have contained it early on.

Dr. Thomas Frieden, the director of the CDC, cites a U.S.-backed program in Uganda to train health workers to diagnose and contain Ebola. It worked. In 2011, a 12-year-old girl there caught the Ebola virus and died from it – but no one else was infected. It was an exceptionally rare Ebola episode that stopped after just a single case.

A similar program in West Africa might likewise have limited the human and financial cost of this outbreak, Frieden noted, adding: “An outbreak anywhere is a risk everywhere.”

This isn’t true only of the Ebola virus. Frieden recalls caring in New York for a patient from India with extensively drug-resistant tuberculosis, a complex case that cost $100,000 to cure. Later, a program was set up in the patient’s native village that could have resolved the case early for $10.

New York hospitals have been on alert for Ebola, but diagnosis and segregation are complicated. I know because I was once such a suspected case.

Years ago, when I lived in Japan, I returned to Tokyo from Congo at the time of an Ebola outbreak there. One night a week later, I came down with a high fever. It felt like malaria, so I made inquiries about what hospital in Tokyo could best treat malaria the next day.

The health authorities heard “Congo” and “fever” and sent an ambulance staffed with people in what looked like spacesuits to rush me to a hospital. My neighbors were taken aback by the scene.

But, at the hospital, the emergency room night doctor knew nothing about tropical diseases. He poked me a bit, shrugged and told me to go home. (The next day, I confirmed that it was malaria.)

So don’t see Brantly and Writebol as reckless curiosities who somehow brought Ebola upon themselves. See them as leaders on the front line of an effort to help and protect Americans and Africans alike. We sometimes forget that health workers can brave significant risks – of infection with HIV, with tuberculosis, or even with the Ebola virus. Indeed, the staff treating Brantly and Writebol in Atlanta volunteered for that duty, and some offered to cancel vacation plans to help.

Bravo to them, and to so many health workers in Africa and America who try to halt the spread of disease – because it’s where humanitarian interests and national interests coincide.

“It’s natural to feel sorry for Kent” Brantly, a former medical school professor of his, Richard Gunderman, wrote in The Indianapolis Star. “But I wonder if Kent wouldn’t turn this around. Instead, he might feel sorry for some of us, at least those of us shaking our heads in dismay at anyone who would travel halfway across the world to do what he did. A ship may be safest in harbor, but that is not what ships are for.”

Contact Kristof at Facebook.com/Kristof, Twitter.com/NickKristof or by mail at The New York Times, 620 Eighth Ave., New York, NY 10018.